1. Field of the Invention
The present invention relates to a zoom lens which is suitable for use in a still camera, a video camera, a silver film camera, a digital still camera and the like, and an optical apparatus having the zoom lens.
More specifically, the present invention relates to a zoom lens having a vibration isolation function in which a lens unit forming a part of an optical system is moved in the direction having a component perpendicular to an optical axis to optically correct a blur of an image caused when the optical system vibrates (or is tilted), thereby obtaining a taken image with no blur.
2. Description of the Related Art
When a photographer riding on a running vehicle or a flying airplane and the like attempts to take an image, vibrations are transmitted to an image-taking system to cause camera shake, resulting in a blur of a taken image. Conventionally, various vibration isolation optical systems have been proposed which have a function of preventing a blur of a taken image (a vibration isolation function).
For example, Japanese Patent Application Laid-Open No. 1981-21133 discloses an optical apparatus which corrects an image blur (isolates vibrations) to obtain an image with no blur by detecting vibrations by a detection means and moving a part of optical members of the optical apparatus in accordance with an output signal from the detection means in such a direction as to cancel out a vibrational displacement of an image due to the vibrations. Japanese Patent Application Laid-Open No. 1986-223819 discloses an image-taking system having a variable apical angle prism disposed closest to an object, in which the apical angle of the variable apical angle prism is varied in accordance with vibrations of the image-taking system to correct an image blur to obtain an image with no blur. In Japanese Patent Application Laid-Open No. 1989-116619 (corresponding to U.S. Pat. No. 5,270,857) and Japanese Patent Application Laid-Open No. 1990-124521 (corresponding to U.S. Pat. No. 5,039,211), an acceleration sensor is used to detect vibrations of an image-taking system, and a lens unit forming a part of the image-taking system is caused to vibrate in a direction perpendicular to an optical axis in accordance with a signal provided from the detection, thereby producing an image with no blur.
Japanese Patent Application Laid-Open No. 1995-128619 discloses a zoom optical system of a four lens unit structure which comprises a first, second, third, and fourth lens unit having positive, negative, positive, and positive optical powers (the power is the reciprocal of a focal length), respectively. The third lens unit includes two lens elements having positive and negative optical powers, respectively, in which the lens element having the positive optical power is caused to vibrate to correct an image blur. Japanese Patent Application Laid-Open No. 1995-199124 (corresponding to U.S. Pat. No. 5,585,966) discloses a zoom optical system of a four lens unit structure which comprises a first, second, third, and fourth lens unit having positive, negative, positive, and positive optical powers, in which the entire third lens unit is caused to vibrate to correct an image blur.
Japanese Patent Application Laid-Open No. 2001-66500 (corresponding to U.S. Pat. No. 6,414,800) discloses a zoom lens of a four lens unit structure which comprises a first, second, third, and fourth lens unit having positive, negative, positive, and positive optical powers. The first, second, and fourth lens units and an aperture stop are moved for zooming, and the entire third lens unit is caused to vibrate to correct an image blur.
In an optical apparatus such as a digital still camera, there are severe restrictions on the overall length of its lens system. When not used (when no image is taken), lens units are generally collapsed and accommodated in the optical apparatus.
When a correction optical system for vibration isolation such as the variable apical angle prism is disposed in the front part of an image-taking system, the presence of the correction optical system of large size in the front part of the optical systems causes problems in terms of space and load on an actuator if the entire lens system is collapsed and accommodated.
In addition, the vibration isolation optical system for providing vibration isolation by using the variable apical angle prism involves large decentering chromatic aberration of magnification in providing vibration isolation especially at a longer focal length.
On the other hand, the vibration isolation optical system for providing vibration isolation by decentering some lenses of the image-taking system in parallel in a direction perpendicular to the optical axis has an advantage of requiring no additional optical system for vibration isolation. However, large decentering aberration may occur in providing vibration isolation to degrade optical performance.
Japanese Patent Application Laid-Open No. 1998-260356 (corresponding to U.S. Pat. No. 6,473,231) discloses an optical system which advantageously achieves high magnifications, but a heavy load is placed on an actuator for moving a first lens unit when it is collapsed due to the large effective diameter thereof.
Japanese Patent Application Laid-Open No. 2001-66500 (corresponding to U.S. Pat. No. 6,414,800) discloses an optical system which advantageously reduces the overall length of the optical system at the wide angle end, but tends to have a frontmost lens unit of large effective diameter since a third lens unit is fixed and each lens unit is not always moved under optimal conditions.